This invention generally relates to a method and apparatus for molding plastic articles. More specifically, the invention relates to a method and apparatus for forming one-piece hollow plastic articles having a blow molded portion and a compression molded portion.
When forming blow molded hollow plastic articles, it is common to extrude a tubular parison from an extrusion head at an elevated molding temperature and in a semi-soft or molten condition. The parison is typically extruded downwardly in the path of a closable blow mold. The mold is usually constructed from a pair of mold halves having inner surfaces that define a mold cavity conforming to the desired configuration of the article. The mold halves close around the parison to clamp it within the molding cavity such that one end is pinched or closed off thereby sealing that end. The other end is closed within the mold halves to form an access opening. With the parison clamped between the mold halves, a blow pin assembly, over which the parison has been extruded, emits air into the interior of the parison which inflates or expands the parison against the molding surfaces of the mold cavity. Heat is conducted by the mold away from the expanded parison causing the plastic to form a solid molded object. The mold halves are then separated and the article removed.
Many blow molded containers are produced having a reduced diameter neck which is molded around the blow pin assembly and held by the mold while the parison body is blown into its final configuration. However, in blow molding containers having relatively wide mouths or access openings, various manufacturing problems can be, and often are, encountered. For example, if a relatively large diameter parison is selected to mold a container having a wide mouth, relatively little radial expansion of the parison is accomplished and folds or imperfect definitions can be obtained on the outer surface of the molded article. Also, a large tear line often forms across the closed end of the container where the parison has been pinched-off. Alternatively, if a small diameter parison is used for a container having a relatively wide access opening, the parison cannot mold itself to the wide mouth access opening without leaving at least a partially annular cap at the opening. This partial cap requires an additional production step to machine the final opening.
When blow molding containers having relatively wide mouths from parisons having relatively small diameters, the molding machine often includes an articulating mechanism that engages and radially stretches the parison, in the mouth area, to conform it with the wide mouth as defined by the mold.
Often it is desirable to form a container having an integral funnel associated with its mouth. When blow molding such a container, additional problems are encountered. Typically the funnel portion of the container is joined to the reservoir or body portion of the container by a relatively narrow neck. As a result, when both the funnel and body of the container are blow molded, considerable flash remains on the molded product in the area of the neck requiring additional trimming or machining operations.
In overcoming some of the problems associated with forming plastic articles of this type, methods which compression mold the funnel while blow molding the remaining portions have been developed. In these molding processes, the mold includes a compression molding surface and a blow molding surface. When the parison is clamped within the mold, a male mold member, having a molding surface corresponding to the compression molding surface, is advanced along the blow pin to compression mold that portion of the container. The remainder or body of the container is then blow molded.
Unfortunately, the prior compression/blow molding apparatuses and procedures are complex and typically require an articulating member which grasps the end of the parison, stretches it over the male mold member. Additionally, the molded article requires additional processing steps to remove excess flash and other material from the molded container.
With the above limitations in mind, it is an object of the present invention to provide an apparatus for molding a hollow plastic article having a compression molded portion and a blow molded portion.
A further object of this invention is to provide a method for molding a hollow plastic article having a compression molded portion and a blow molded portion.
A related object of this invention is to provide an apparatus and method in which the molded article is compression molded, blow molded and trimmed all in a single step of the molding operation.
Another object of this invention is to produce an article having integral funnel connected by a narrower neck to a relatively wide body.
Still another object of this invention is to provide an apparatus and method for producing an article in which an integral funnel portion is formed by compression molding and while the body portion of the article is formed by blow molding.
In accomplishing the above objects, the present invention provides both an apparatus and method for producing a hollow plastic article having both a blow molded portion and a compression molded portion. The article includes a relatively wide body, a narrower neck, and a relatively wide funnel-shaped mouth. In forming the article, a plastic parison, having a downwardly facing open end and a diameter which is larger than the diameter of the funnel, is downwardly extruded from an extrusion head. The parison is extruded from the extrusion head and then enclosed within the mold whose mold cavity includes surfaces defining a blow molded portion and a compression molded portion of the article. Once the parison has been clamped within the mold, a blow pin is moved into position for blow molding and a male mold member, associated with the blow pin, is moved to cause its molding surface, which corresponds to the compression molding surface of the mold, to engage the parison thereby compression molding the funnel portion of the container. Air is admitted through the blow pin expanding the remainder of the parison into conformity with the blow molding surfaces of the mold. A cutting member is then moved relative to the mold until its cutting edge severs the parison at a position immediately adjacent to the compression molded funnel. The finished article is then removed from the mold.